The fact that an additive is a flame retardant does not necessarily mean that it will have good smoke retardant properties, as is well known to those skilled in the art. U.S. Pat. Nos. 3,821,151, 3,845,001 and 3,870,679 teach use of certain molybdenum compounds, alone or on combination with other compounds, as smoke retardants in PVC. The specific compounds listed therein suffer from the disadvantages that most, such as MoO.sub.3, are colored compounds giving an unsatisfactory tint to compositions in which they are used. Even white or lightly colored molybdenum compounds such as the ammonium or sodium molybdates tend to discolor the PVC compositions, and also give less satisfactory smoke reduction than MoO.sub.3.
New, highly effective smoke retarded polymer compositions are desired.